In research and development of robot technology, it is one of important issues how an object is reliably controlled by a robot hand. With respect to an operation of grasping an object by a robot hand, specifically, not only detecting a grasping force to grasp the object but also detecting a shearing stress occurring to the hand surface due to the grasping operation is needed for reliable control of the robot hand. The reason of this is that detecting a frictional force caused between the object and the hand surface by the shearing stress contributes to exerting optimum frictional force control to fulfill reliable control of the object.
In recent years, tactile sensors aimed at detecting such a shearing stress have been being developed (see Patent Literature 1, for instance). An example of such conventional tactile sensors will be described below with reference to a schematic perspective view shown in FIG. 8.
As shown in FIG. 8, a tactile sensor 501 has a configuration in which a plurality of piezoresistive cantilevers 502 (cantilevers having piezoresistors on hinges thereof) formed from a thin film of about several hundred nanometers are placed in a film-like elastic body 503 so as to be independent of one another.
The cantilever 502 has one end formed as a fixed portion and the other end formed as a movable portion that can be deformed only in a thicknesswise direction of the thin film forming the cantilever 502. The cantilevers 502 are each electrically connected to a control unit, not shown, through terminal parts and interconnections that are not shown. When a shearing force or a pressure is exerted on a surface of the film-like elastic body 503, for instance, a shearing stress or a compressive stress produced inside the film-like elastic body 503 causes the movable portions of the cantilevers 502 to be moved and deformed, thus making it possible to detect the shearing force or the pressure. In order to detect shearing stresses or compressive stresses acting on the film-like elastic body 503 in various directions, the cantilevers 502 are arranged in the film-like elastic body 503 so that the movable portions thereof differ in direction of deformation, for example, so that the directions of the deformation are set along X-axis, Y-axis and Z-axis directions as shown in the drawing.
When the film-like elastic body 503 is brought into contact with an object or the like, the tactile sensor 501 configured in this manner is capable of detecting shearing stresses or compressive stresses that are produced in various directions in the film-like elastic body 503, by the cantilevers 502. Such a film-like elastic body 503 is formed of PDMS (polydimethylsiloxane), for instance, as material that is easily elastically deformed by application of an external force.
Hereinbelow will be described a method of manufacturing the tactile sensor 501 having such a configuration.
As shown in a schematic illustration of FIG. 9, an SOI wafer 510 having, e.g., two cantilevers 502 formed thereon is placed in a container 517 with the wafer supported by a spacer 516 formed of PDMS. After that, fluidized elastic body PDMS 519 is injected into the container 517, as shown in FIG. 9. The injection of the PDMS 519 is performed in such a manner that at least the cantilevers 502 and fixed parts of the cantilevers 502 on the SOI wafer 510 are immersed and embedded in the injected PDMS 519.
After the PDMS 519 injected into the container 517 is subsequently cured, parylene layers 518, as strength-reinforcing members, deposited on a surface of the SOI wafer 510 exposed from the PDMS 519 are partially removed by O2 plasma etching process, for instance.
Subsequently, an etching process is performed from a top face of the container 517, so that Si layers 511 and SiO2 layer 512 are removed which are exposed from the PDMS 519 and which are sacrifice layers of the SOI wafer 510. As a result, as shown in FIG. 10, the fixed parts of the cantilevers 502 on the SOI wafer 510 are removed, so that recesses 520 are formed on the surface of the PDMS 519. By the removal of the sacrifice layers that have fixed the cantilevers 502, accordingly, the individual cantilevers 502 are arranged independently of one another in the PDMS 519.
After that, as shown in FIG. 11, fluidized PDMS 519 is injected into the recesses 520 formed on the surface of the PDMS 519, so that PDMS 519 is resupplied. After this resupply, the injected PDMS 519 is cured, and the film-like elastic body 503 formed of the PDMS is formed, so that the tactile sensor 501 is finished.
Patent Literature 1: JP 2007-218906 A